Many science subjects have the need for students to learn laboratory skills, such
techniques as titrations, extractions, digestions, gravimetric determinations, to name
but a few. Within my own discipline of food science it is desirable that the students
are aware of the techniques required to determine the basic composition of foods
through chemical analysis. The term Proximate Composition refers to the
percentage of the five macronutrient components present in our foods, namely:
protein, fat, carbohydrate, moisture and total minerals.
The analytical procedures which are used to determine these proteins, fat, moisture
and minerals can be carried out in a three hour practical session (carbohydrates can
be determined by difference from 100%). Working with about 20 students in a
laboratory session, I run a demonstration/practical in which we carry out the
analysis of peanuts. I start the session with a preamble along the lines:
“There are two reasons that students undertake practical work, the first is to gain
marks which help them to get a degree and the second is learn laboratory
techniques. In this session I am only interested in the second.”
We then get started on the fat extraction, the protein digestion, the moisture and ash
determinations. There is then a ½ hour gap during which they go for a coffee
break. After this we carry out titrations on the protein digest and distil off the solvent
which has been used to extract the fat. All this fits into a 2½ hour period. I tell the
students that to complete the procedures they will need to return the next morning to
obtain their moisture and mineral results (these take about 12 hours in an oven or
furnace).
Towards the end of the practical session I inform the students that they are required
to complete a report. For their report, I tell them that they each have a unique set of
data which is within the expected variation for analysis of peanuts, but includes a
random element to ensure that each student has a unique set of figures. I go on to
tell them how to access the data using the program which I developed.
Despite the students not actually working with the laboratory data, I suggest that
they return the following day for the final moisture, ash and fat results, if only to see
the analytical part of the practical to completion....